In semiconductor apparatuses, such as electronic devices, the application of a technology related to terahertz waves is desirable. In order to generate terahertz waves, the oscillation wavelength may be increased by using a quantum cascade laser, or the operation frequency may be increased in an electronic device. Electronic devices capable of handling such high frequencies include Esaki diodes and resonant tunneling diodes (RTDs).
An Esaki diode utilizes the interband quantum tunneling, and is formed of, for example, a pn junction of p+-InGaAs 511 and n+-InGaAs 512, which are heavily doped with an impurity, as illustrated in FIG. 1A. With this structure, when a voltage is applied, as illustrated in FIG. 1B, a current increases at first since electrons flow through a thin junction portion due to quantum tunneling, however, as the voltage increases, the flow of electrons is gradually blocked and the diode exhibits a property of having a negative resistance.
An RTD is formed, as illustrated in FIG. 2A, for example, such that i-InAlAs 523, i-InGaAs 524, and i-InAlAs 525, which are not doped with impurities, are formed between two compounds, n-InGaAs 521 and 522. The compounds i-InAlAs 523 and 525 are made of a material having a wider bandgap than the n-InGaAs 521 and 522. In the RTD, a quantum level is formed in the i-InGaAs layer 524. With this structure, as illustrated in FIG. 2B, when a given voltage is applied, a large current flows, however, as the voltage increases, the RTD exhibits a property of having a negative resistance.
Since the Esaki diode and the RTD exhibit a property of having a negative resistance as described above, they may be used in oscillators.
An example of the above-described related art is disclosed in Japanese Laid-open Patent Publication No. 5-48076.